Exhaust-gas recirculation (EGR) systems are used in internal combustion engines to reduce the emissions of the internal combustion engine, for example with regard to nitrogen oxides. Cooling of the recirculated exhaust gases by means of the exhaust-gas cooler positioned in the EGR system further reduces the NOx emissions.
High pressure EGR systems have been developed to reduced emissions and increase combustion efficiency. In high-pressure EGR systems, exhaust gas to be recirculated is drawn from an exhaust line upstream of a turbine of the turbocharger and is supplied to the internal combustion engine at its inlet side. Exhaust-gas aftertreatment devices such as for example, a catalytic converter and/or a particle filter (diesel particle filter), may also be arranged in the exhaust line. In such an example, an EGR valve may be the component which, in interaction with a bypass valve, controls or affects an exhaust-gas recirculation rate through the EGR line. The exhaust gas flowed through the EGR system may be cooled via an EGR cooler positioned in an EGR line, before it enters the inlet side internal combustion engine. The EGR cooler reduces the exhaust-gas temperature and thereby increases the density of the exhaust gas. As a result of which the exhaust-gas recirculation cooler also contributes to an increased EGR rate. As a further result of the cooling of the hot exhaust gas to be recirculated, the temperature of the cylinder fresh charge is also reduced, that is to say the cooling of the exhaust gas contributes to improve charging of the combustion chamber with fresh air or fresh mixture.
However, the Inventors have recognized several drawbacks with the aforementioned EGR system. For example, after a cold start during the warm-up phase of the internal combustion engine, increasing the operating temperature of the internal combustion engine quickly may increase combustion efficiency as well reduce engine internal friction. Therefore, cooling of the exhaust gas in a high pressure EGR system may not be desired during a warm-up phase in the aforementioned EGR system as it would reduce intake charge temperature unnecessarily. Further, it may be desirable to reduce the emissions of unburned hydrocarbons and the emissions of carbon monoxide resulting from an incomplete combustion as a result of excessively low cylinder temperatures and increase the exhaust-gas temperature such that exhaust-gas aftertreatment systems arranged downstream of the cylinders in the exhaust-gas discharge system may reach its light-off temperature (e.g., operating temperature) more quickly. Therefore, the cooling of the exhaust gas during the recirculation is therefore prevented in the warm-up phase of the internal combustion engine described above to enable the exhaust-gas aftertreatment device to reach as desired operating temperature and to reduce engine emissions. For this purpose, the EGR apparatuses in some EGR systems may be provided with a bypass valve which enables the EGR cooler to be bypassed during the recirculation of the exhaust gas and which may be arranged upstream or downstream of the EGR valve in the exhaust-gas recirculation line.
WO 2009/022113 A1 discloses a high-pressure EGR system for in an engine, in which exhaust gas is extracted directly from an exhaust line upstream of a turbine of a turbocharger and is supplied via an EGR line to two exhaust-gas coolers connected in series. After exiting the second exhaust-gas cooler as viewed in the flow direction, the cooled exhaust gas is supplied to the inlet side of the internal combustion engine. The two exhaust-gas coolers are designed differently in terms of their cooling efficiency, such that the first exhaust-gas cooler has a lower cooling power than the second exhaust-gas cooler. The exhaust gases to be recirculated are thus cooled in a stepped fashion, to a required temperature level of the exhaust gases to be introduced into the intake-air line. WO 2009/022113 A1 also discloses a method in which recirculated exhaust gas is inhibited from flowing through the second exhaust-gas cooler in a warm-up phase of the internal combustion engine.
Furthermore, many modern internal combustion engines generate relatively little heat, which on the one hand is extremely positive with regard to thermal loading, but which secondly is disadvantageous with regard to the warm-up phase of the internal combustion engine, because this can lead to increased friction within the engine during the warm-up phase. Furthermore, auxiliary heating devices may be needed, for example, in order to meet the requirements of a cabin heating arrangement.
Some internal combustion engines may be configured to recover the heat energy of the exhaust gases of the internal combustion engine in order thereby for example to shorten the warm-up phase of the internal combustion engine, wherein exhaust gases are conducted through a separate exhaust-gas heat exchanger which is arranged, for example, in an exhaust line downstream of the exhaust-gas aftertreatment devices. In this way, the heat of the exhaust gases may be transferred to the heat exchanger medium circulating in the heat exchanger. The heat exchanger medium may be coolant of the internal combustion engine, such that in this way the warm-up phase of the internal combustion engine can be influenced by a warming thereof via the relatively warm cooling medium. The heated coolant may also be flowed to a cabin heating arrangement, enabling heating of the cabin during warm-up.
Both of the aforementioned systems, that is to say the exhaust-gas recirculation system and the heat recovery system, are provided separately from one another and, with their components, require a considerable amount of installation space, which is available only to a restricted extent in or on motor vehicles.